It is well established that vision depends on a complex network of brain regions. Although visual processing has been extensively studied in a range of subcortical and neocortical regions, little is known about visual processing in higher-order, multimodal areas of the medial temporal lobes (MTL). Recent work has indicated that specific MTL subregions (e.g., the hippocampus and perirhinal cortex)-which are traditionally associated with memory processes- play a critical role in online visual processing. For instance, our recent studies have demonstrated that MTL damage can impair processes that support scene perception and visual short-term memory. These surprising findings have opened up many important questions about which visual processes are supported by the MTL, about the roles of different MTL subregions in visual cognition, and about how different memory and visual processes interact. The central idea behind this application is to address these fundamental questions with a combination of studies examining patients with focal lesions to specific MTL subregions, high-resolution functional magnetic resonance imaging (fMRI), and model-based analyses of results obtained with novel psychophysical paradigms. The studies aim to determine the role of the MTL in complex visual perception and visual short-term memory, and to determine how the processes involved in perception and visual short-term memory tasks interact with episodic memory. The application uses a unique 'parallel lesion/fMRI approach' in which studies of MTL lesion patients and high-resolution neuroimaging studies of healthy subjects allows conclusions about the involvement of different regions in healthy subjects, and about whether such regions play a necessary causal role in these behaviors. In addition, the proposed studies will be the first to utilize high-resolution imaging of the MTL in perception and short-term memory tasks and will utilize a novel combination of parametric psychophysical methods with neuroimaging methods, and so promise to provide novel insights into the visual processes supported by substructures of the MTL not previously possible. The proposed studies are significant because they challenge current models to explain MTL involvement across perception and memory paradigms, and thus will provide richer and more theoretically constraining results than previously possible. In addition, the studies have important translational implications because they will provide a more complete characterization of the cognitive deficits associated with temporal lobe damage suffered by various psychiatric and neurological populations. By identifying the cognitive processes supported by these regions, the proposed studies can lead to the development of targeted rehabilitation strategies that better capitalize on both the disrupted and the spared functions in such patients.